The present invention relates generally to an improved composition and method for repairing metal reinforced concrete structures, and more particularly to such a composition and method specifically adapted for application as a slurry or other workable blend to surfaces of damaged concrete structures containing metal reinforcements. The composition of the present invention employs a mortar/aggregate and fiber reinforcements mixture containing a quantity of migratory corrosion inhibitors. The mixture is particularly adapted for repairing the surfaces of concrete structures, while at the same time for use in passivating and otherwise protecting the surfaces of metal reinforcements present in damaged concrete structures over extended periods of time. The environmentally friendly migratory corrosion inhibitors are preferably a mixture of sodium gluconate and an alkali metal sebacate such as sodium sebacate and/or potassium sebacate with ammonium benzoate being suitable as an alternate to the sebacate. In accordance with the present invention, the migratory corrosion inhibitors may be present from two sources, one source being the addition of the inhibitors to the mortar/aggregate blend, the second source being contained in an extruded reinforcing plastic fiber comprising a polymeric resin matrix into which a quantity of the migratory corrosion inhibitors set forth above has been co-extruded. It will be appreciated that the repair coatings of the present invention may be applied to a wide variety of structures involving various types of structures. Therefore, it may be appropriate to select an aggregate of relatively fine particulate material for certain applications, while utilizing somewhat coarser aggregates for other applications. Those of skill in the art will, of course, be able to select the appropriate aggregate for given applications.
The migratory corrosion inhibitors present in the improved formulation, preferably sodium gluconate and sodium sebacate are applied to a damaged surface area of a concrete structure as components of a fiber reinforced patch material, with the migratory corrosion inhibitors from either or both sources being released to the concrete structure over a relatively extended period of time. The formulation is suited for application in slurry or suspension form either directly by utilizing a trowel and normal rendering tools or with a spray rendering machine.
The overall composition is typically prepared in separate containers or vessels as a two-component system, the first of the two components consisting of a ready-mix powder comprising the mortar mix and co-extruded fiber reinforcement, the second being a liquid resin in the form of a water dispersion of non-toxic polymers or plasticizers and containing a quantity of the migratory corrosion inhibitors as set forth above. Prior to use, the contents of these two containers or vessels are mixed together to form the slurry or other workable suspension which is then ready for surface application.
Following application, the slurry hardens to form a durable fiber reinforced protective layer or coating which has excellent mechanical properties including a high level of adhesion, cohesion, durability and impermeability to water and carbonation attack. The coating also has a desirable low modulus of elasticity. In addition to these mechanical properties, the coating provides excellent corrosion protection to metal reinforcement present in the damaged concrete structure, thus providing protection in the patch area as well as in the area surrounding the patch. The compositions of the present invention accordingly increase the quality, enhance the appearance, and also extend the life of the damaged concrete structure, particularly at the repair site, as well as in the area immediately surrounding the site.
The migratory corrosion inhibitor molecules from either source evolve out of the body of the hardened coating as the coating and the concrete structure forming the substrate continue to age. While the inhibitors which have been incorporated directly into the blend may evolve rapidly, those incorporated as a component in the co-extruded fiber generally evolve at a less rapid rate. Regardless of their course of derivation, these molecules migrate through the porous channels of the concrete structure to provide ongoing protection to the metal reinforcements, such as, for example, steel rods, mesh, and cable. The inhibitors selected for the current application possess the characteristic of being able to migrate through cured concrete and onto and along the surfaces of the metallic members. The combination of the corrosion inhibitors when present in the surface coating deliver long-term corrosion protection to the structure while retarding the rate of corrosion on the steel reinforcements.
As indicated hereinabove, the second source of migratory corrosion inhibitors is an extruded fiber comprising a polymeric resin matrix into which a quantity of migratory corrosion inhibitors has been co-extruded. The co-extruded inhibitors preferably include sodium gluconate and sodium sebacate, although ammonium benzoate may be incorporated as an alternative to the sebacate component or gluconate component.
Thus, the composition and methods of the present invention provide a medium for both immediate as well as ongoing metallic surface protection through extended delivery of migratory corrosion inhibitors to and through damaged concrete surfaces. The features of the invention are achieved through the addition of these inhibitors directly to the mortar mix/fiber reinforced composition employed in the working formulation of the coating. The utilization of impregnated reinforcing fibers as either the primary or secondary source of migratory corrosion inhibitors provides an additional measure of extended long-term corrosion inhibitor availability.
The improved composition and method of application in accordance with the present invention offers engineers, property owners, contractors, DOTs and other governmental agencies a corrosion inhibiting technology adapted to extend the life of reinforced concrete structures. The composition and formulations of the present invention enable the artisan to undertake otherwise difficult repairs or restorations on substrates having smooth surfaces and to which good adhesion is normally difficult if not impossible to achieve. Such repairs are also rendered possible where high build-up or thick coatings may otherwise be required.
Because of the nature of the improved compositions, the coatings may normally be applied to surfaces without requiring that the repair area initially soaked with water or otherwise be rendered wet. Furthermore, the thixotropic qualities of the improved composition along with its accelerated thickening capabilities enable application of multiple coats, thereby reducing labor costs.
Because of the physical and chemical nature of the migratory corrosion inhibitors present in the formulations, these inhibitors form a protective layer or deposit directly onto metallic surfaces. In addition to those areas which are in direct contact with the coating, the migratory properties of the inhibitors extend protection to metallic surfaces surrounding or otherwise adjacent the repair area. In addition to protection afforded the metallic components, the mechanical properties of the fiber reinforced coating, when hardened, protects the surface of the concrete repair area against further carbonation or attacks by chlorides and/or acid rain.
Given the advantageous features of the composition and method of application, the working formulations of the present invention may be utilized in combination with reinforced, precast, pre-stressed, post-tensioned or marine concrete structures. Such structures include, by way of example, steel-reinforced concrete bridges, highways, streets, parking decks, ramps, and garages exposed to corrosive environments such as carbonation, deicing salts, and possible atmospheric attack. The excellent water resistant properties of the hardened or set material permit its application to concrete piers, piles, pillars, pipes and utility poles, and in general may be utilized to restore and repair virtually any type of reinforced concrete, commercial and/or civil engineered structures.